Eur. Phys. J. D (2013) 67: 47
https://doi.org/10.1140/epjd/e2013-30569-8

Regular Article

Potential energy curves, spectroscopic constants and spin-orbit coupling: A theoretical study on twelve triplet Λ-S states of Ge₂ molecule

¹ College of Physics and Electronic Engineering, Henan Normal University, Xinxiang 453007, P.R. China
² College of Physics and Electronic Engineering, Xinyang Normal University, Xinyang 464000, P.R. China

^a e-mail: scattering@sina.com.cn

Received: 13 September 2012
Received in final form: 25 November 2012
Published online: 7 March 2013

Abstract

The potential energy curves (PECs) of twelve triplet Λ-S states and fourteen Ω states generated from five triplet Λ-S states of Ge₂ molecule are calculated by an ab initio quantum chemical method. The PEC calculations are made for internuclear separations from 0.15 to 1.10 nm using the complete active space self-consistent field method, which is followed by the internally contracted multireference configuration interaction approach with the Davidson modification (MRCI  +  Q). The basis set used here is the aug-cc-pV5Z-pp. Convergent behavior is discussed and excellent convergence is observed with respect to the basis sets and level of theory. The PECs are extrapolated to the complete basis set limit by the total-energy extrapolation scheme. The spin-orbit coupling effect is accounted for by the Breit- Pauli Hamiltonian in combination with the aug-cc-pVTZ-pp basis set. With the PECs, the spectroscopic parameters are evaluated by fitting the first ten vibrational levels, which are obtained by solving the ro-vibrational Schrödinger equation using Numerov’s method. The spectroscopic results are compared with those reported in the literature. Excellent agreement with available measurements is found. The vibrational levels and inertial rotation constants are calculated for each Λ-S state and those of the first ten vibrational states are reported for the non-rotation Ge₂ molecule. The spectroscopic parameters of the 1³Σ_u⁺, 1³Δ_u, 2³Σ_u⁺, 1³Π_g, 2³Π_g, 3³Π_g, 1³Σ_u⁻, 2³Σ_u⁻, 2³Π_u and 2³Σ_g⁻ Λ-S states and the vibrational levels and inertial rotation constants of all the Λ-S states determined by the MRCI  +  Q/Q5 calculations are expected to be reliable predicted ones.